Nanoparticles are ubiquitous and by far the most abundant particle-like entities in natural environments on Earth and are widespread across many applications associated with human activities. There are many types of naturally occurring nanoparticles and man-made (engineered) nanoparticles. Nanoparticles occur in air, aquatic environments, rain water, drinking water, bio-fluids, pharmaceuticals, drug delivery and therapeutic products, and a broad range of many industrial products. Nanoparticles usually occur within polydisperse assemblages, which are characterized by co-occurrence of differently-sized particles.
Given the widespread usage of nanoparticles, the ability to control and accurately characterize their properties may be useful to many applications. Conventional methods for measuring nanoparticle properties may be inaccurate for polydisperse samples of mixed nanoparticle sizes, which are common in many applications. Some of these conventional approaches make measurements on an ensemble of a large number of nanoparticles within a sample. Because the light scattered from all nanoparticles is measured simultaneously, it may be difficult to resolve the nanoparticles into their constituent sizes when there is a range of particle sizes. Other approaches fail to account for the large differences in the intensity of scattered light produced by differently-sized nanoparticles across the range of nanoparticle sizes. In these approaches, the low scattering signals from small nanoparticles may be undetected, or the high scattering signals from larger nanoparticles can obscure the signals from smaller nanoparticles. As a result of these deficiencies, the concentration of nanoparticles of any given size, and hence the entire size distribution, can be subject to unknown error.
These methods of detecting nanoparticles are commonly referred as dark field microscopy. The instrument to perform such an analysis typically comprises a small cell (for example a cuvette) that enables illumination of a liquid with a precisely-defined, narrow light sheet and observation of scattered light from the nanoparticles, usually at a 90-degree angle relative to the light sheet plane. In other words, the direction of observation is perpendicular to the direction of the plane of illumination. Different sizes of particles can be visualized via the camera capturing light scattered by particles, with images having different sizes and intensities (various brightness of pixels) depending on the size of the particles. But as noted above, recording images of light scattered by particles of mixed sizes coexisting in a solution remains somewhat problematic due to the huge difference in the amount of light scattered by particles of different sizes. Specifically, the intensity of scattered light depends very strongly on particle size, changing by many orders of magnitude between 10 nm and 1000 nm diameter nanoparticles, for instance. This problem is also encountered in other areas of photography and videography and is commonly called High Dynamic Range (HDR) imaging. What has been needed is an improved system and method that overcomes the problems that tend to be inherent in dark field microscopy systems.
In U.S. Published Patent Application No. 2015/0346076 A1 to Stramski et al., published Dec. 3, 2015 (“Stramski”), the entirety of which is incorporated herein by reference, these problems were addressed by using several light sources and a single color camera recording simultaneously several different colors of scattered light by the Bayer pattern of pixels corresponding to the three additive primary colors conventionally used in photography. In the Stramski approach, final images were obtained from a single recording device and hence images of the same colloidal volume at different colors were recorded in the same area of the recording device or sensor, thereby resulting in pixel numbering relative to a single point of origin, usually being one of the corners of a sensor in the camera. This made processing images in different colors possible because positions of observed particles were given in the same system of coordinates. However, when multiple sensors are used, the images may become unaligned relative to each other, and Stramski did not address alignment.
What is needed, therefore, is an improved system that overcomes or avoids the alignment problems presented by using multiple detectors that cannot easily be aligned to the exact same point.